![]() The most accurate (and straightforward) way to calculate target uptime is to figure out your recovery point objective (RPO) and recovery time objective (RTO). So how should you calculate those 9s for your use case? Should you provide three, four, or even six 9s of uptime? ![]() If you commit to five 9s (99.999%) of uptime, your service can only be down 5.25 mins per year. If your 24×7 service guarantees three 9s (99.9%) of uptime, then it can still be unavailable up to 8.76 hours a year. How should high availability be measured, then? Well, it can be measured by defining and committing to a certain uptime that’s part of your availability SLA (Service Level Agreement). For instance, disks can be corrupted, or an application instance can crash due to a memory overflow caused by a sudden load spike. Even if a company claims that “our service is here for you 24×7”, in reality, that service runs on software and hardware that can’t provide the same guarantees. Sooner or later, every system experiences a failure or an outage. However, disaster recovery techniques are still relevant when discussing details of the failover process. This article focuses on how you can make a PostgreSQL deployment highly available by eliminating a single point of failure. High availability refers to a system’s ability to operate continuously by removing the possibility of a single point of failure.ĭisaster recovery is the process of getting the system back to normal operations after a failure or outage. ![]() ![]() Both relate to and influence each other during an application’s design and development, but HA differs significantly from DR. High availability should not be confused with disaster recovery (DR). So, walk through the options for a highly available deployment of PostgreSQL and then you can make a choice that fits your use case.ĭifference Between High Availability and Disaster Recovery Why several and not one? Well, there’s no silver bullet or one-size-fits-all solution when it comes to high availability and PostgreSQL. Let’s review several popular solutions that increase the high availability of PostgreSQL deployments and, as a result, the availability overall of your application. With that in mind, you may be wondering which PostgreSQL high availability (HA) deployment option is best for your application. INSERT INTO COMPANY VALUES (10, 'James', 45, 'Texas', 5000.Ensuring your application can handle failures and outages is crucial, and the availability of your application is only as good as the availability of your PostgreSQL instance. Now, let us create three more records in COMPANY table using the following INSERT statements − This would produce the following result − Testdb=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME If you want to know the total amount of salary of each customer, then GROUP BY query would be as follows − ExampleĬonsider the table COMPANY having records as follows − Make sure whatever column you are using to group, that column should be available in column-list. You can use more than one column in the GROUP BY clause. The GROUP BY clause must follow the conditions in the WHERE clause and must precede the ORDER BY clause if one is used. The basic syntax of GROUP BY clause is given below. The GROUP BY clause follows the WHERE clause in a SELECT statement and precedes the ORDER BY clause. This is done to eliminate redundancy in the output and/or compute aggregates that apply to these groups. The PostgreSQL GROUP BY clause is used in collaboration with the SELECT statement to group together those rows in a table that have identical data.
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